Multilayer polymeric optical films are widely used for various purposes, including as mirrors and polarizers. Multilayer optical films can be prepared by multiple alternating layers such as a first birefringent polymeric material layer alternated with a second isotropic polymeric material layer. Alternatively, the first and second polymeric materials may both be orientated provided that there is a sufficient difference in refractive index mismatch between the first and second layers.
As described for example in U.S. Pat. No. 5,612,820, copolymers and blends may be used to provide an extremely wide variety of different refractive indicies which may be matched or provide optimum polarizing effect. Additionally, the use of copolymers and miscible blends of polymers may be used to enhance the processability of the alternating layer during coextrusion and orientation. Further, the use of copolymers and miscible blends permits the adjustment of the stress optical coefficients and glass transition temperatures.